The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Internal combustion engine vehicles that employ automatic transmissions may include a torque converter positioned between the engine and the transmission of the vehicle. A torque converter is a fluid coupling device typically including an impeller coupled to an output shaft of the engine and a turbine coupled to the input shaft of the transmission. The torque converter uses hydraulic fluid to transfer rotational energy from the impeller to the turbine.
The rotational speed of the impeller relative to the turbine in the torque converter is typically different so that there is a converter slip therebetween. Because large slips between the engine output and the transmission input significantly affect the fuel economy of the vehicle, some vehicles employ a torque converter clutch (TCC) for controlling or reducing the slip between the engine and the transmission. The TCC can also mechanically lock the impeller at the output of the engine to the turbine at the input of the transmission so that the engine and transmission rotate at the same speed. Locking the impeller to the turbine is generally only used in limited circumstances because of various implications.
Thus, a TCC generally has three modes. A fully locked mode, a fully released mode and a controlled slip mode. When the TCC is fully released, the slip between the impeller and the turbine of the torque converter is only controlled by the hydraulic fluid therebetween. In the slip mode, the slip between the torque converter impeller and turbine is set so that it does not exceed a predetermined amount by controlling the pressure of the hydraulic fluid in the TCC. Rapid changes in throttle request result in rapid changes to engine speed and torque applied to the torque converter. Rapid increases in engine speed and/or torque can result in torque converter clutch slip or TCC slip changing from a controlled value to an excessive value that is desirably controlled back to a controlled value.
When the TCC is operating in the slip mode, one method to control slip in the torque converter is known as Electronic Controlled Capacity Clutch (ECCC) control. ECCC control utilizes feed forward control of TCC torque to control torque converter slip to a desired value or range, for example, based upon fuel economy and noise, vibration and harshness (NVH) targets and the operation of the powertrain. Smaller slip values can improve fuel efficiency under certain conditions, while larger slip values can improve NVH and drivability issues under certain conditions.